In an environment of intensive global competition, robot-centered cells are playing more and more important roles in incorporating automation and repetitive processing for improving productivity and quality. The robotic-centered cell, also called as the robotic cell, is a manufacturing cell in which loading and unloading operations are performed by one ore more robots. The robotic cell usually includes a series of workstations, and one or more robots. Amongst the workstations, one acting as a feed-in device is configured to feed into work pieces to be processed; another acting as a feed-out device is configured to output the processed work pieces; and other workstations functioning as processing workstations performs processing operations on work pieces in a fixed sequence. In the meantime, the one or more robots are responsible for transporting the work pieces within the cell from one processing workstation to another.
Only for a purpose of illustration, FIG. 1 illustrates a pictorial diagram for a general robotic cell in the prior art. As illustrated in FIG. 1, it is clear that the robotic cell 100 includes m workstations 110-1 to 110-m and n robots 120-1 to 120-n. In FIG. 1, for a purpose of simplification, a feed-in device, a feed-out device and processing workstation are generally illustrated as workstation without being differentiated clearly, however, it should be noted that the robotic cell 100 usually comprise all of a feed-in device, processing workstations and a feed-out device. The robotic cell 100 is normally in a flow-shop type, and in a cyclic production, each work piece usually passes through finite workstations in the same order.
For performance of the robotic cell, a direct and widely used measure of efficiency is for example productivity, particularly throughput of the cell, i.e., the number of finished parts produced per unit time slot. How to achieve the maximum/near-maximum throughput in a robotic cell, even a small improvement in throughput, is always a highlighted objective, especially in communication, computer and consumer electronics (3C) industry.
In the above-mentioned cyclic production, the cycle time is referred to the duration during which the sequence of the movements and operations are completed in a normal iteration to produce the work piece. Thus, maximizing the throughput is to pursue the minimum cycle time.
In the existing cell layout determination, it usually uses a try-and-error-loop but time-consuming working loop and in FIG. 2 is schematically illustrated a flow chart of an example cell layout determination for a robotic cell in the prior art. As illustrated in FIG. 2, initial placement of workstations is set at step S201; then based on the initial placement of the workstations, an operation path is determined and an operation sequence is created at step S202; and afterwards possible travelling paths between each pair of workstations are defined. Subsequently, the reachability and path feasibility are checked based on predetermined check rules at step S203 and after that, the cycle time is obtained by for example, cell simulation or cell running, if it is determined at step S206 that the performance requirement is met, the process is ended, otherwise at step S207, the placement of the workstations and/or the sequence of the operations in a robotic cell are rearranged by empiristic trials. Next, operations of steps S204 to S207 may be performed repeated until the performance requirement is met. However, from the example flow chart, it may be noticed that the cell layout determination process is severely dependent on the experience of engineers, and it just like buying a lottery on the cycle time performance, due to lack of efficient means.
In the prior art, there was proposed to improve the cycle time to produce a part by determining arrangement of workstation in a cell or optimizing the scheduling in the robotic cell. However, these methods are mainly directed to a robotic cell with a simple cell layout, and when facing a robotic cell comprising many robots and workstations, it is still hard to achieve a productivity improvement for a robotic cell in an efficient way.